1. Field of the Invention
The present invention relates to an impedance measuring apparatus for measuring based on a bioelectric impedance method a body constitution such as a body fat rate representing a rate of fat weight to total human body weight, a body fat mass representing an absolute weight value of the fat, or a total body water volume, and, in particular, to a safety countermeasure for preventing an element of the measuring apparatus from making an undesirable effect on a human body when a circuit element in the measuring apparatus has failed.
2. Description of the Prior Art
Conventionally, it has been known that the body constitution can be estimated by measuring a bioelectric impedance, as described in The American Journal of Clinical Nutrition, 41(4) 810-817 1985 xe2x80x9cAssessment of fat-free mass using bioelectrical impedance measurement of the human bodyxe2x80x9d. As for a method for measuring body fat mass contained in a human body by employing this mechanism, there has been known a method for measuring body fat mass in which an impedance between body ends such as hands and feet is measured by a four terminal electrode method and the body fat mass is determined by combining the measured impedance value with personal body information such as weight, height, sex, age, etc., and further an apparatus for measuring the weight of a person to be measured together with the body fat mass simultaneously is disclosed by the Japanese Patent Publication No. Hei 5-49050. Various apparatuses employing this mechanism have already spread in market.
These conventional body fat meters are generally configured as shown in FIG. 5 of the accompanying drawings.
FIG. 5 is a block diagram briefly illustrating a configuration of a general body fat meter employing the bioelectric impedance method. The body ends of a person to be measured, or a right and a left hands or feet are brought into contact with current electrodes 72A, 72B and voltage electrodes 73A, 73B. When a measurement start switch in a switch group 87 is pressed, a measuring current or an alternating current of about 50 kHz and of about 500 xcexcA is generated by a current supply section 81 in response to a signal from a CPU 80. This alternating current is the measuring current and is applied through the current electrodes 72A, 72B to the body of a person to be measured, and then a voltage value between the voltage electrodes 73A, 73B is detected by a voltage detecting section 82, and thereby a bioelectric impedance value is determined. A body fat rate or a body fat mass is estimated based on preset body information of the person to be measured and the determined bioelectric impedance value, and the result thereof is displayed on a display circuit 88. The current supply section 81 and the voltage detecting section 82 to which these electrodes 72A, 72B, 73A, and 73B are connected are composed of a plurality of electronic components such as amplifiers (operational amplifiers), resistors, and capacitors.
A battery 89 is connected to a constant voltage supply section 90, where a rated voltage (Vdd and xe2x88x92Vdd) is generated and output to drive the overall measuring circuit, that is, the constant voltage supply section 90 is connected to respective ICs including CPU 80 to supply a constant voltage. This constant voltage supply section 90 generally employs a three terminal regulator or the like.
As described above, the body fat meter according to the bioelectric impedance method is configured such that electrodes are directly brought into contact with the skin of the person to be measured and the body fat rate and the body fat mass are measured by actually applying a small alternating current to a human body during the measurement.
However, since various electronic components are employed in the current supply section 81 and the voltage detecting section 82 as described above, and these electronic components are precisely configured, they are likely to fail if these circuits and components are subjected to such loads as static electricity, high temperature, or the like, and further the terminals of these electronic components may be separated from the substrate if the body fat meter is dropped. In such cases, the current cannot be correctly controlled, and subsequently a current greater than expected may possibly be applied to the human body through the respective electrodes 72A, 72B, 73A, and 73B.
Since a human being is a creature having a sensory organ, applying a current greater than a certain level to the body may cause a person to feel numbness or pain. FIG. 1 of the accompanying drawings is a table showing the current effect on a human body, classified by a category and a level of the current. This table indicates that a human body begins to sense a current and to react thereto when a current greater than 1 mA is applied. As the current increases, the initial slight pain turns into a strong pain. A current of about 20 mA is regarded as a limit current, which a human being can endure and from which he or she can escape by himself or herself.
Since FIG. 1 shows a case for an adult male with a current applied for one second, similar conditions for females and children may be observed at considerably lower currents than these values.
As described above, when an excessive current greater than a certain level is applied to a human body, the body is subjected to a heavy load. Accordingly, an electric instrument is desired to be equipped with a safety countermeasure for preventing a negative effects caused thereby, and especially in a body fat meter which determines a bioelectric impedance value by applying a current to the human body, an improvement is desired from the viewpoint of electrical safety.
For this safety countermeasure, it is generally contemplated as one method that the measuring current applied to the human body is continuously detected and the circuit power supply is turned off when the current exceeds a specified level. Further, it is contemplated as an alternative method that the measuring current is limited by adding a high resistor between a measuring circuit section and an electrode plate.
Although several safety countermeasures including those described above can be contemplated to prevent an abnormal current from being applied to the human body when a circuit element of a body fat meter employing the bioelectric impedance method has failed or a life thereof has run out, the one method described above to turn off the power supply in case of a current greater than a specified level being applied makes the circuit configuration of the overall measuring apparatus complicated and demands more components, which results in the cost increase of the apparatus.
Though the circuit configuration is simple in the alternative method described above which employs a high resistor installed between the measuring circuit and the electrode, the circuit for measuring the bioelectric impedance has a higher resistance than the impedance of the human body, and this has negative effects on measurement errors, and finally results in a decreased accuracy in measuring the body fat rate and the body fat mass.
The present invention is made in the light of these problems described above and the object thereof is to provide a safety countermeasure against an abnormal condition which may be caused by an excessive current applied to the human body when the element has failed or broken, using a simple circuit configuration without decreasing the accuracy in measuring the bioelectric impedance, and also to provide a bioelectric impedance measuring apparatus equipped with a safety countermeasure enabling an estimation of an index relating to body constitution such as body fat mass, total body water volume.
According to an aspect of the present invention, there is provided a bioelectric impedance measuring apparatus which has a plurality of electrodes to be brought into contact with the skin of a person to be measured, a measuring circuit section which is connected to said plurality of electrodes and applies an alternating current to the body of the person and measures the bioelectric impedance, determines a bioelectric impedance value based on the bioelectric impedance analysis and estimates an index regarding the body constitution of the person, said apparatus characterized in that
a set of a capacitor and a resistor arranged parallel with each other is installed between each of said electrodes and said measuring circuit section.
According to another aspect of the present invention, there is provided a bioelectric impedance measuring apparatus which has a plurality of electrodes to be brought into contact with the skin of a person to be measured, a measuring circuit section which is connected to said plurality of electrodes and applies an alternating current to the body of the person and measures the bioelectric impedance, determines a bioelectric impedance value based on the bioelectric impedance analysis and estimates an index regarding the body constitution of the person, said apparatus characterized in that
at least one set of a capacitor and a resistor arranged parallel with each other is installed between said electrodes and said measuring circuit section.
According to another aspect of the present invention, there is provided a bioelectric impedance measuring apparatus which has a plurality of electrodes to be brought into contact with the skin of a person to be measured, applies an alternating current to the body of the person, a current supply circuit and a voltage measuring circuit which is connected to a plurality of electrodes, determines a bioelectric impedance value based on the bioelectric impedance analysis and estimates an index regarding the body constitution of the person, said apparatus characterized in that
a set of a capacitor and a resistor arranged parallel with each other is installed between each of voltage measuring electrode among said electrodes and said voltage measuring circuit.
According to another aspect of the present invention, there is provided a bioelectric impedance measuring apparatus which has a plurality of electrodes to be brought into contact with the skin of a person to be measured, applies an alternating current to the body of the person, a current supply circuit and a voltage measuring circuit which is connected to a plurality of electrodes, determines a bioelectric impedance value based on the bioelectric impedance analysis and estimates an index regarding the body constitution of the person, said apparatus characterized in that
a set of a capacitor and a resistor arranged parallel with each other is installed between at least one voltage measuring electrode among said electrodes and said voltage measuring circuit.
According to another aspect of the present invention, there is provided a bioelectric impedance measuring apparatus which has a plurality of electrodes to be brought into contact with the skin of a person to be measured, applies an alternating current to the body of the person, a current supply circuit and a voltage measuring circuit which is connected to a plurality of electrodes, determines a bioelectric impedance value based on the bioelectric impedance analysis and estimates an index regarding the body constitution of the person, said apparatus characterized in that
a set of a capacitor and a resistor arranged parallel with each other is installed between each of current supply electrodes among said electrodes and said current supply circuit.
According to another aspect of the present invention, there is provided a bioelectric impedance measuring apparatus which has a plurality of electrodes to be brought into contact with the skin of a person to be measured, applies an alternating current to the body of the person, a current supply circuit and a voltage measuring circuit which is connected to a plurality of electrodes, determines a bioelectric impedance value based on the bioelectric impedance analysis and estimates an index regarding the body constitution of the person, said apparatus characterized in that
a set of a capacitor and a resistor arranged parallel with each other is installed between at least one current supply electrode among said electrodes and said current supply circuit.
According to an embodiment of the present invention, a set of a capacitor and a resistor arranged parallel with each other is further installed between each of voltage measuring electrodes among said electrodes and said voltage measuring circuit.
According to another aspect of the present invention, there is provided a bioelectric impedance measuring apparatus which has a plurality of electrodes to be brought into contact with the skin of a person to be measured, a measuring circuit section which is connected to said plurality of electrodes and applies an alternating current to the body of the person and measures the bioelectric impedance, determines a bioelectric impedance value based on the bioelectric impedance analysis and estimates an index regarding the body constitution of the person, said apparatus characterized in that
between each of said electrodes and said measuring circuit section, a capacitor is installed close to said electrode and a diode for electrostatic safety countermeasure is installed close to said measuring circuit.
According to another aspect of the present invention, there is provided a bioelectric impedance measuring apparatus which has a plurality of electrodes to be brought into contact with the skin of a person to be measured, a measuring circuit section which is connected to said plurality of electrodes and applies an alternating current to the body of the person and measures the bioelectric impedance, determines a bioelectric impedance value based on the bioelectric impedance analysis and estimates an index regarding the body constitution of the person, said apparatus characterized in that
between each of said electrodes and said measuring circuit section, a set of a capacitor and a resistor arranged parallel with each other is installed close to said electrode and a diode for electrostatic safety countermeasure is installed close to said measuring circuit.
According to an embodiment of the present invention, the said capacitor is a ceramic capacitor.
There will now be described in detail preferred embodiment of the present invention with reference to the drawings.